Calcium-induced interactions of calmodulin domains revealed by quantitative thrombin footprinting of Arg37 and Arg106

Calmodulin acts as an intracellular calcium receptor in calcium-induced switching in eukaryotic cells. Calmodulin's ligation states were examined using thrombin footprinting techniques, with each ligand state analysed for energetic and structural properties. Calcium saturation protected the Arg37 and Arg106 sites from proteolysis. The susceptibility/protection of ligands was dependent on the level of calcium and the sites to which the calcium binds.